The regulation of the temperature due to heat generated inside the housing of an electronic device is an important consideration during the design of an electronic device. Cooling is important because if left unchecked, heat can cause electronic components to malfunction during use or lead to premature component failure. As improvements in processor size and speed occur, the amount of heat generated by the larger and faster processors also increases. Additionally, improved processors require larger power supplies and auxiliary components that generate increased amounts of heat and require improved systems for heat removal.
Another factor that aggravates the need for improved heat removal cooling systems is the trend towards making portable computing devices such as laptops, personal data assistant's (PDA'S) and handheld computing devices smaller and thinner. The trend toward smaller and thinner electronic devices having larger, faster processors renders the traditional heat removal cooling systems inadequate for several reasons. First, smaller devices having faster processors result in an increased density of heat producing electronic components leading to higher localized concentrations of heat. Also, a decreased amount of space is available for localized temperature regulating devices such as traditional heat sinks. Lastly, a decreased amount of space is available to create ventilation paths that pass by heat sources.
One such cooling device is a passive heat sink. In such a device a heat sink is formed from a material, such as aluminum, which readily conducts heat. The heat sink is usually placed on top of and in physical contact with the component.
One method of increasing the cooling capacity of these heat sinks is by including a plurality of cooling fins that are physically connected to the heat sink. These fins serve to increase the surface area of the heat sink and, thus maximize the transfer of heat from the heat sink to the surrounding atmosphere. In this manner the heat sink draws heat away from the component and transfers the heat into the surrounding air.
In order to further enhance the cooling capacity of a heat sink device an electrically powered blower (an axial fan may serve as the blower) is often mounted within or on top of the heat sink. In operation the fan forces air to move past the fins of the heat sink, thus cooling the fins by enhancing the transfer of heat from the fins into the surrounding atmosphere. As air flows by the fins, heat can be drawn from the component into the heat sink at a faster rate. The fan typically draws air into the heat sink from the top, passes the air over the fins, and exhausts the air in the vicinity of the bottom. Accordingly, the exhaust air is hotter than that of the intake air.
There are known devices of this type, for example, U.S. Pat. No. 6,196,300 “Heat sink”. The device described in this US patent comprises an axial fan with hub and blades that produces a flow passing by heat exchanging channels of the heat sink. The majority of inlets to the heat exchanging channels are located just opposite the axial fan's impeller with a certain number of said channels being placed radial in relation to fan axle.
The axial fan produces a sufficiently high air pressure. However, due to the weak airflow in the area adjacent to fan axle, the conditions for cooling the central part of the heat sink located underneath the hub are unfavorable. In this case non-uniform cooling of the heat sink and electronic component will take place allowing for bad conditions for the heat exchange process.
Centrifugal blowers are used more rarely in cooling device designs for the purpose of producing airflow.
Specifically, U.S. Pat. No. 5,838,066 “Miniaturized cooling fan type heat sink for semiconductor device” offers a design employing a centrifugal blower that is installed to the side of the heat sink. In one particular embodiment of this invention the cooling airflow passes by rectilinear means through the heat exchanging channels of the heat sink.
However, placement of a centrifugal blower to the side of the heat sink increases the devices size and reduces its effectiveness. This is because the location of the centrifugal blower leads to insufficient coordination between the direction of channel inlets and direction of airflow supplied from the blower. The loss in airflow energy results in the reduction of airflow speed in the heat exchanging channels and the reduction of heat exchange efficiency. A portion of energy is also expended as friction against the casing that encloses the blower.
An invention described in the patent of Japan No. 8-195456 entitled “Cooler for electronic apparatus”. This device comprises a centrifugal fan enclosed in the casing and installed above the heat exchanging channels that are made divergent. Another heat sink surface is made so that the possibility of thermal contact with an electronic device is provided. The inlet of the centrifugal fan faces the heat sink. The fan produces an airflow that passes by the heat exchanging channels and then gets drawn into the inlet of the centrifugal fan. Since this centrifugal fan operates by drawing air in through the heat sink, there is an area in the central part of the heat sink that receives poor air circulation. Adding to this problem, the airflow first passes through the elongated heat exchanging channels gathering heat along the way from the channels surfaces. As the air approaches the central part of the heat sink its cooling ability is decreased due to the reduced temperature differential between the preheated channel air temperature and the surface temperature at the center of the heat sink. This results in inefficient cooling of the heat sink's central surface area and uneven cooling of the heat sink in general. This is the area where the electrical component is transferring the most heat to the heat sink and where the greater differential between the two is most important. To help overshadow this problem, one has to increase the fans power resulting in an increased airflow but not solving the initial problem. In addition to the heat dissipation problems, the device is considerably large due to the centrifugal fans placement above the heat sink. An electric drive is yet placed above the centrifugal fan increasing the coolers overall size even more.
Additionally, traditional fan assemblies are less effective in removing heat when used in smaller, thinner devices.
It is known cooler for electronic devices that uses cross flow fans (see U.S. Pat. No. 6,227,286 FIGS. 15A–15C and 40A–40C). Using this type fan gives the possibility to suck and discharge air at the sides of the fan; therefore the thickness of the apparatus can be reduced. The design described in this invention has pour efficiency because there is a hub inside the fan impeller where the fan motor is located.
It is also known another cross flow cooling device for semiconductor components that uses cross flow fans (see U.S. Pat. No. 6,047,765). This device needs an electric motor mounted at a shaft outside of an impeller, therefore increasing dimensions of the cooling device.
Thus, it would be generally desirable to provide an apparatus that overcomes these problems associated with fan assisted heat sink devices.